Interpolymers of vinylidene chloride and diacrylate esters of a glycol



desirable properties.

United States Patent 3,317,450 INTERPOLYMERS 0F VINYLIDENE CHLORIDE AND DIACRYLATE ESTERS OF A GLYCOL Dallas G. Grenley, Midland, and Harold J. Townsend,

Saginaw, Mich., assignors to The Dow Chemical Company, Midland, MiclL, a corporation of Delaware No Drawing. Filed Mar. 14, 1963, Ser. No. 265,064 6 Claims. (Cl. 26029.7)

This invention relates to the preparation of flexible webs coated with plastic coatings. More particularly, it relates to the preparation of such coated webs which exhibit little or no tendency to block.

By blocking is meant the tendency of two web surfaces to resist slippage or sliding past each other. With thermoplastic coatings, such as are involved in the present invention, blocking is to some extent temperature dependent. The block temperature then is the minimum temperature at which two surfaces of the web in face-toface contact will not slip apart when placed under an applied pressure for a time which is arbitrarily selected. The block temperature is of significance when the webs are rolled up on themselves and are shipped and stored in such manner. Likewise, after conversion to bags and pouches, the block temperature assumes an importance not only in shipping and storing but also in feeding into package filling apparatus. For most commercial applications it has been found that this block temperature should be at least 140 F. when placed under an applied pressure of one pound per square inch for 24 hours.

Flexible webs, such as paper and transparent plastic films, have come to be used in ever increasing amounts in the packaging and allied arts. For such uses, the webs must satisfy a wide diversity of requirements. As it turns out, many of the common webs that are economical enough for consideration for packaging uses fall short of meeting one or more of those requirements. The deficiencies of those flexible webs have been overcome in the past by laminating or coating polymeric, resinous materials to the flexible web. Such coatings and laminations have provided increased abrasion resistance, improved the barrier properties, and otherwise upgraded the flexible Web to where it is commercially acceptable. It is commonplace for certain saran coatings to be applied to those flexible webs to improve the barrier properties, particularly to moisture and to gases. The sarans that have been used for this purpose have been those of the class commonly referred to as the normally crystalline vinylidene chloride polymers. This class consists of those polymeric materials composed of at least 70 percent vinylidene chloride together with at least one monoethylenically unsaturated comonomer. 'As the vinylidene chloride content of the copolymer is increased, the barrier properties generally will also increase. However, that increase is usually accompanied by a loss of. flexibility and other In coating flexible webs, the saran coating must be soft enough to have comparable physical properties to the flexible web substratum but must still have enough vinylidene chloride present to realize the desired barrier properties. In order to achieve the former, however, when the saran must be soft enough to approximate the properties of the flexible web, it has been found that the coatings block or stick together under relatively mild pressures. That tendency has limited the use of the normally crystalline vinylidene chloride polymers.

It would, therefore, be desirable to have and, accordingly, it is the principal object of this invention to provide improved, flexible webs coated with continuous, organic, resinous coatings.

It is a further object to provide such webs wherein the coatings are of a normally crystalline vinylidene chloride polymer having superior barrier properties.

Patented May 2, 1967 "ice It is a still further object to provide such webs wherein the coatings are non-blocking.

It is yet another object to provide compositions useful for preparing such coatings for flexible webs.

The above and related objects are attained by means of coated, flexible webs consisting of continuous, coherent, flexible webs coated with a continuous, adherent coating comprising an interpolymer of (a) vinylidene chloride, (b) from about 0.5 to about 5 percent by weight of the interpolymer of a diacrylate ester of a glycol having the formula:

wherein n is an integer from 1 to about 6 and wherein said glycol has an average molecular weight below about 270, and (c) any remainder being of at least one monoethylenically unsaturated comonomer wherein said interpolymer is composed of at least 70 percent by weight vinylidene chloride. The invention further comprehends coating compositions comprising an aqueous latex of the the above-identified interpolymer.

The flexible web substrata utilizable in the present invention include plastic films prepared from organic, thermoplastic, resinous materials, such as the polyolefins, including typically polyethylene, polypropylene, copolymers of ethylene and propylene, polystyrene, rubber hydrochloride, and other known similar materials. Known thermoplastic film materials including regenerated cellulose, cellulose ethers and esters, such as ethyl cellulose and cellulose acetate, may also be used. Other flexible web substrata, such as paper, may likewise be employed in the presently claimed concept.

As indicated, the invention finds utility with all flexible webs. The materials of the substrata must be water insoluble, since the coating is to be applied from an aqueous medium. Although the concepts of the present invention may be employed with semi-rigid and even with rigid objects, the earlier-mentioned problems are usually of less magnitude and consequence with such materials than with the flexible webs. The invention, however, is equally applicable to such materials.

As is known in the art, it is frequently desirable to improve the adherence of coatings to many flexible webs to use a primer undercoat or anchoring coat of known composition. Thus, with regenerated cellulose it has been known to be desirable to coat the regenerated cellulose substratum with urea formaldehyde or other coatings prior to the application of the saran barrier coating. It is also known to utilize coatings of styrene/butadiene copolymers in a capacity of an anchor coat. Other useful anchor coats for any given substratum will be known.

The flexible web substrata are commercially available or may be readily preparedin the case of the resinous materials by thermal extrusion, casting, or other known technique.

The coating to be applied to the flexible web is of an interpolymer composed essentially of at least two monomeric components. In order to achieve the requisite barrier properties, it is necessary that the interpolymer contain at least 70 percent by Weight of vinylidene chloride interpolymerized therein. Although somewhat less vinylidene chloride may be used, it is done with a sacrifice in the barrier properties and other properties and characteristics associated with the sarans. The second essential monomeric component is a diacrylate ester of a glycol. Those diesters are of glycols having the formula:

wherein n is an integer from 1 to about 6 and wherein said glycol has an average molecular weight below about 270. When the diester is prepared from a glycol having a molecular weight higher than that indicated, the resulting vinylidene chloride interpolymer is less likely to be non-blocking and also will have a somewhat reduced barrier property. Typical of such esters are ethylene diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, and pentaethylene glycol diacrylate. Mixtures of those acrylates may likewise be used. In such mixtures there may be included higher members of the polyglycols having individually higher molecular weights than 270. The average molecular weight of the mixture, however, must remain below about 270.

When only the two essential components are present, it will frequently be found that the compositions, when coated on the flexible web, will be too brittle for most uses. Consequently, it is desirable and, in fact, preferable to interpolymerize one or more comonomers with the above-mentioned two essential monomeric components. Representative of useful comonomers are vinyl chloride, vinyl acetate, acrylonitrile, alkyl acrylates and methacrylates, and vinyl alkyl ethers. The choice of comonomers will be dictated in large measure by the properties and characteristics desired in the final interpolymer.

The coatings are deposited from aqueous latexes of the above interpolymers. Those latexes may be prepared by using conventional emulsion polymerization technology. Typically, the monomeric materials are dispersed and emulsified in a continuous, aqueous phase containing a water-soluble polymerization catalyst and an emulsifying agent for the monomeric materials in water. Polymerization is induced and maintained by subjecting the emulsion to elevated temperature until polymerization is substantially complete. The latex is then filtered to remove pre-coagulum. Any additives, which are to be incorporated, such as stabilizers, to increase the mechanical and storage stability of the latex, are incorporated and the latex is then ready for use. If desired, the usual additives employed in the latex art including typically pigments, dyes, plasticizers, light and heat stabilizers, antioxidants, and the like may be incorporated into the latex.

The improved, flexible webs are attained by depositing a wet film coating of the latex on the flexible web substratum and subsequently drying and coalescing that wet coating into a continuous, adherent coating. The wet coating may be applied by conventional means including doctoring, spraying, brushing, dipping, or the like. As such, the coating compositions are adaptable for use with existing coating apparatus and equipment.

The coated webs that result exhibit the desired properties including barrier properties of the saran compositions but with reduced blocking tendency over saran compositions lacking the diacrylate ester.

The present inventive concept will be illustrated by the following example wherein all parts and percentages are by weight.

Example Two latexes were prepared at 50 percent polymer solids by conventional emulsion polymerization. In one latex the monomer charge consisted of 85 percent vinylidene chloride, 11 percent acrylonitrile, and 4 percent Z-ethylhexyl acrylate and was used for comparative purposes. In the other latex, the monomer charge was 84.5 percent vinylidene chloride, 11 percent acrylonitrile, 4 percent 2- ethylhexyl acrylate, and 0.5 percent ethylene diacrylate.

Films were cast from each of the latexes by known techniques and their resistance to blocking determined by placing a folded piece of film in an oven at various temperatures under a weight of one pound per square inch for 16 hours. The comparative specimen blocked at F. The film of this invention did not block at F.

The same results are observed when the latexes are coated on various substrata, such as regenerated cellulose, polystyrene film, cellulose acetate film, polyethylene film, and kraft paper. In each instance the barrier properties of the coated web remains equivalent to the comparable saran composition without the diester but with substantially reduced blocking tendencies. Likewise, the same comparisons with the above control are noted when the diester is of any glycol having a molecular weight less than about 270.

What is claimed is:

1. A coating composition for coating flexible webs with non-blocking coatings comprising an aqueous latex of an interpolymer consisting essentially of (a) vinylidene chloride, (b) from 0.5 to about 5 percent by weight of a diacrylate ester of a glycol having the formula:

wherein n is an integer from 1 to about 6 and wherein said glycol has an average molecular weight below about 270, and (c) any remainder being of at least one monoethylenically unsaturated comonomer and wherein said interpolymer is composed of at least 70 percent by weight vinylidene chloride.

2. The composition of claim 1 wherein said diacrylate ester is ethylene diacrylate.

3. The composition of claim 1 wherein said interpolymer is composed of 84.5 percent vinylidene chloride, 11 percent acrylonitrile, 4 percent 2-ethylhexyl acrylate, and 0.5 percent ethylene diacrylate.

4. A flexible web having on at least one surface a nonblocking, continuous, adherent, barrier coating comprising an interpolymer of (a) vinylidene chloride, (b) from 0.5 to about 5 percent by weight of a diacrylate ester of a glycol having the formula:

wherein n is an integer from 1 to about 6 and wherein said glycol has an average molecular weight below about 270, and (c) any remainder being of at least one monoethylenically unsaturated comonomer and wherein said interpolymer is composed of at least 70 percent by weight vinylidene chloride.

5. The flexible web of claim 4 wherein the substratum is regenerated cellulose.

6. The flexible web of claim 4 wherein the substratum is paper.

References Cited by the Examiner UNITED STATES PATENTS 2,320,536 6/1943 Pollack et a1. 26089.5 2,413,973 1/1947 Howk et a1. 260-895 2,824,025 2/1958 McIntyre 117-144 SAMUEL H. BLECH, Primary Examiner.

MURRAY TILLMAN, Examiner.

J ZIEGLER, Assistant Examiner. 

1. A COATING COMPOSITION FOR COATING FLEXIBLE WEBS WITH NON-BLOCKING COATINGS COMPRISING AN AQUEOUS LATEX OF AN INTERPOLYMER CONSISTING ESSENTIALLY OF (A) VINYLIDENE CHLORIDE, (B) FROM 0.5 TO ABOUT 5 PERCNET BY WEIGHT OF A DIACRYLATE ESTER OF A GLYCOL HAVING THE FORMULA: 